1. Field of the Invention
The present invention relates to a fluid pump suitable for moving a fluid, such as air or liquid.
2. Description of the Related Art
A piezoelectric pump of the related art is disclosed in International Publication No. 2008/069264. FIGS. 1A-1E illustrate a pumping operation of the piezoelectric pump disclosed in International Publication No. 2008/069264 in a third-order resonance mode. The piezoelectric pump includes a pump body 10, a diaphragm 20 having an outer peripheral portion thereof fixed to the pump body 10, a piezoelectric element 23 attached to the central portion of the diaphragm 20, a first opening 11 formed in the pump body 10 that faces a portion at or near the central portion of the diaphragm 20, and a second opening 12 formed in an intermediate area between the central portion and an outer peripheral portion of the diaphragm 20 or formed in the pump body 10 that faces this intermediate area. The diaphragm 20 is made of a metal plate, and the piezoelectric element 23 has a size such that the first opening 11 is covered but it does not to reach the second opening 12. A voltage having a predetermined frequency is applied to the piezoelectric element 23 so as to cause a portion of the diaphragm 20 that faces the first opening 11 and a portion of the diaphragm 20 that faces the second opening 12 to bend and deform in directions opposite to each other. As a result, a fluid is sucked into one of the first opening 11 and the second opening 12, and is discharged from the other one of the second opening 12 and the first opening 11.
A piezoelectric pump, such as that shown in FIGS. 1A-1E, has a simple structure so that it can be formed as a thin pump. Accordingly, the piezoelectric pump is used as, for example, an air transport pump in a fuel cell system.
However, electronic devices into which such a piezoelectric pump is integrated are becoming smaller, and accordingly, it is also desirable to reduce the size of a piezoelectric pump without decreasing the capabilities (flow rate and pressure) of the pump. Moreover, in accordance with a reduced power supply voltage of an electronic device into which a piezoelectric pump is integrated, it is desirable to reduce a drive voltage. As the size of a piezoelectric pump or the drive voltage decreases, capabilities (flow rate and pressure) of the pump are decreased. Accordingly, when using a piezoelectric pump having a structure of the related art, there are limitations on reducing the size of the piezoelectric pump while maintaining capabilities of the pump and on enhancing capabilities of the pump without increasing the size of the piezoelectric pump.
In a fluid pump provided with a diaphragm of the related art, an increase in the size of the diaphragm is effective for increasing the flow rate. This, however, causes not only an increase in the size of the entire fluid pump, but also an increase in the generation of audible sound because of a low operating frequency.